<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>fixed宽度相当于谁的</title>
    <style>
        .fa{
            width:150px;
            height:150px;
            background-color: #cad53d;
        }
        .fa div{
            position: fixed;
            width:100%;
            height:100%;
            background-color: blue;
        }
    </style>
</head>
<body>
<div class="fa">
    <div></div>
</div>
</body>
</html>